12v Touch Switch Exciter Circuit - This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits. It can support a cable length of about 2500 feet. A typical remote switch circuit is also shown as well as a receiver circuit for those switches.. . . Circuit by David Johnson P.E.-February, 2002 175Khz Inductive Pulse Receiver - This circuit is discussed in more detail in the Experimenters Journal. The receiver’s six inch diameter coil detects the ring signal from the above transmitter and use a single NPN transistor to provided enough amplification for the signal to be easily viewed on an oscilloscope. . . Circuit by Dave Johnson P.E.-July, 2000
1uS Light Pulse Receiver + Post Amp - This circuit is designed to detect very weak light pulses lasting 1uS. It uses a tuned LC feedback network to provide high sensitivity while giving high ambient light immunity. A post voltage amplifier is included with a gain of about X20. The circuit is described in more detail in the receiver section of my Handbook of Optical Through the Air Communications. Note: The LF357 op amp is no longer available, this circuit is for reference only.. . . Circuit by Dave Johnson P.E.-March, 1999
2 Cell Lithium Ion Battery Charger - This circuit was build to charge a couple series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. The charger operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage __ Designed by Bill Bowden
2 Line Telephone Line Status Indicator - Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive. . . Circuit by David A. Johnson P.E.-June, 2000
2 Transistor Oscillators - This page has two unusual two-transistor oscillators. I set the component values for a low frequency application. Both circuits draw only about 1 micro amp of current. . . Circuit by Dave Johnson P.E.-December, 2002
3 Level Audio Power Indicator - Battery-operated3 LED display that connect it to loudspeaker output __ Contact: Flavio Dellepiane, fladello @ tin.it
3 Volt Low Battery Voltage Flasher - This circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment. . . Circuit by David A. Johnson P.E.-January, 1998
36-Hour Watchdog Timer - A watchdog timer is often used in computer systems to detect when a computer is hung up and is no longer running properly. If it does become locked up and is not able to supply a reset pulse to the circuit within a defined time frame the timer times out a. . . Circuit by David A. Johnson P.E.-April, 2010
4 Line Telephone Line Status Indicator - Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. . . Circuit by David A. Johnson P.E.-June, 2000
50 MHz Frequency Counter Voltage Meter & SwR/PWR Indicator - This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876 __ Designed by Aleksander Stare
7-segment Display Water-Level Indicator - This water-level indicator uses a 7-segment display, instead of LEDs, to indicate the water level (low, half and full) in the tank. Moreover, a buzzer is used to alert you of...__ Electronics Projects for You
AC Current Indicator LightThis circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being drawn by a load. It is especially useful for remote lights, where you may not . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005
AC Indicator-Self PoweredOften there is a need to monitor when AC current flows into a load. The circuit below works well for this application. It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser. A wire carrying the AC current is . . . Hobby Circuit designed by David Johnson P.E.-December, 2007
AC Power Indicator
-
The AC powerline indicator presented here has a complete
galvanic isolation from the grid. The indicator is an LED
that lights up when a current flows, although the current
can be measured more accurately with an AC voltmeter set to
its mV rangemust register on this site [Designer: Published
in Elecktor July/Aug, 2010]
Acceptable Voltage IndictorI have used this circuit many times in custom test fixtures where a simple go-no go indication was needed. The circuit can also be used to adjust a particular voltage be within specific high or low limits. The three LEDs will indicate if the voltage is. . . Circuit by David A. Johnson P.E.-February, 2002
Active AC Power Line IndicatorThe circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow. It is powered by a 3v CR2032 lithium coin cell. I. . . Circuit by David A. Johnson P.E.-May, 2005
Alarm Beeps when the “Check Engine” Light Turns OnWhen wired into a car’s indicator light panel, this circuit will turn on a loud beeper when the “check engine” light turns on. . . Circuit by David Johnson P.E.-July, 2006
Alkaline Low Battery Voltage IndicatorIn many battery powered systems a user would like to know when it was time to replace the batteries before they were completely discharged, causing the device being powered to fail completely. Alkaline batteries have an open cell voltage of about 1.5 volts. As they are discharged, the voltage slowly drops. When the cell voltage reaches about 1.25v, they have delivered about 90% of their stored energy. . . Circuit by David A. Johnson P.E.-June, 2012
Automotive Electrical Voltage Indicator This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present.. . . Circuit by David Johnson P.E.-July, 2006 |